Apparatus for precipitating and filtering



1,634 720 July 1927' L. D. MILLS ET AL APPARATUS FOR PRECIPITATING ANDFILTERING Filed May a. 1924 5 Sheets-Sheet 1 July 5, 1927.

1.. D. MILLS ET AL APPARATUS FOR PRECIPITATING AND FILTERING Filed May8. 1924 5 Sheets-Sheet 2 l VEITITORS fiwwz/ 1,634,720 July 1927' L.MILLS ET AL APPARATUS FOR PRECIPITATING AND FILTERING Filed May 8, 19245 Sheets-Sheet 5 Patented July 5, 1927.

UNITED STATES PATENT OFFICE.

. LOUIS 1). runs, or annwoon CITY, AND means 18. cnownor' PALO ALTO,CALI- roams, ASSIGNORS 1 THE MERRILL COMPANY, or sm'rmcrsco, CALIFORNIA,

- A CORPORATION OF CALIFORNIA.

APPARATUS FOR PRECIPITATIIIG FILTERING.

Application filed May 8,

The invention relates to" apparatus for precipitating and filteringvaluable substances from solutions (and particularly metallic substancesfrom metallifero us soludeposited, and the general object of theinvention is to provide an apparatus which avoid difliculties and lossesincident to the operation of the processes and apparatus heretoforeknown and insure more effective and complete precipitation and recovery.

The invention, has to do particularly with providing for and utilizingthe deposit in a particular manner of solids upon the filtering mediumthrough which the solution is moved. In many cases, asin the preciptation of, gold and silver from cyanide solutions, the finalprecipitation is effected as the solution flows through the layer ofsolids collected 'on the filter surface. We have found that theefficiency of this operation is largely increased by forming a layer ofparticular character, which is here designated equalized, meaningtherebynot merely a layer of substantially uniform permeability, butmore particularly a layer wherein the comparative y fine particles aredistributed with the comparativel coarse particles throughout the layerin suc substantial uniformity that the solution passing. through thelayer at any part thereof comes in 1ntimate contact therewith. In manycases, as, for instance, in the precipitation of gold and silver fromcyanide solutions, using zinc as the precipitant, the particles formingthe layer are ch1efly particles of precipitate, the precipitate beingmore efi'ectrveto complete the precipitation than thepreciprtant,presumably because each partlcle thereof constitutes a couple; and theinvention rovides for exceptionally effective contact 0 the solutiontherewith. The invention avoids the necessity for unduly expensiveapparatus p and wasteful consumption of precipitant involved in sundryprocesses heretofore sug "gested.

In the practice of the mventlon, the solution containing the precipitantis preferably caused to circulatein such manner that the heavier solidsdo not settle, wholly within 14 is tapered to prevent lodgm 1924..Serial No. 711,928.

a filter tank, in contact with theentire filtermg area of the filteringmedium, as by flowing over it in one direction, and so that thecirculating solution does not disturb or agitate the surface of thesolution toentrain a1r therein.

The preferred type of a rying out the invention is 1 lustrated in theaccompanyin drawings in which Fig. 1 is a longitudina section throughone form of apparatus, with the ancillary apparatus indicateddiagrammaticially;'Fig. 2 is a trans- ,yerse' section through theapparatus shown in Fig. 1; Flg. 3. is a top plan of the apparatus; Fig.4 1s a View simllar to Fig. 1 of a modified form of apparatus; Fig. 5 1sa lan of the apparatus shown in Fig. 4; and ig. 6 is a section throughone of the filter units.

' The form of apparatus shown in Fig. 1.

comprises a rectan lar filter tank 10. having a series .of fi ter units11 ."suspended therein and supported in place by means of the ledges 12ig. 2) projecting inwardly from the bottoms of the sides of the aparatus. In the illustrated embodiment o the invention the filter unitsare of the vacuum leaf type, but it will be understood that theinvention is not to be limited to this type e0 paratus for caroffiltration inasmuch as it is equally applicable to pressure filtrationvpracticed within closed vessels. Vacuum leaf filtration is preferred inmost instances because it permits of cheaper construction and theoperations are more easily observed. The general features ofconstruction and mode 'of operation of the filter units 11 are wellknownand need 'no detailed description.

The filtering medium 13 6) may be canvas or other suitable material, thetwo sides ofeach filter unit being secured to the cross-bar 14 andseparated by strips 15 of wood, cocoa'mattin or the-l1ke to'provideproper drainage. he top of the support ent of solids thereon. Theperforated pipe 16 of each filter unit is detachably connected b acoumtake of the pum 19 for drawing the solution through the lter leaves.The clarified solution to be treated is con tained in tank 21, whence itis caused to pass into the steady-head tank 22 through a vacuum tank 20in which a vacuum is maintained by pump 26. The maximum or upling 17with the pipe 18 which lea s to the the upper part of the tank. Thebafiies 42 per solution level 23 in tank 22 and tank 10 is kept constantby the float controlled valve 24 in the inlet pipe 25, and the minimumor lower solution level 27 is controlled by a float 28 which operatesan' electrical contact 29 to stop the motor 35 connected with the pumps19 and 26 when the solution reaches the low level 27. The steady-headtank 22 is connected by the pipe 30 with the filter tank 10. As thesolution flows from the steady-head tank into the bottom of the filtertank it is supplied with a precipitant. The precipitant (preferably zincdust when gold and silver are recovered from cyanide solutions) issupplied from a feeder 31 to a mixing cone 32 which receives solutionfrom the pump 19 through the pipe 33. Thus a continuous stream in whichthe precipitant is contained, substantially an emulsion, passes down thepipe 34 into the pipe 30. The parts shown diagrammatically are of usualconstruction and mode of operation.

The means for effecting a homogeneous mixture of the coarser and finerparticles of the solids in the solution in thefilter tank 10 and therapid distribution of the homogeneously mixed particles in equalizedlayers over the entire area of the filter surfaces, comprise avertically arranged cylindrical conduit or passagewa 37 locatedsubstantially in the middle 0 the filter tank 10, as shown in Fig. 3,and a propeller 38 arranged in the upper part of the conduit. Thepropeller 38 is mounted on the lower end of a vertical shaft 39 drivenfrom a shaft 40 connected with any convenient source of power. Thepropeller 38 acts to draw the solution in the tank 10 upwardly throughthe conduit 37 and to discharge it through .the openings 41 and againstthe baflles 42 and 43 hinged to cross-pieces 44 secured to and 43 serveto deflect the solution so that it will flow down through thepassageways 45 between the filter units 11. The bafiles also prevent thesolution discharged throu h the upper end of the conduit from distur ingand rupturing the surface of the liquid in the tank. Thus the absorptionof air in the solution from this cause is prevented.

The solution discharged over the upper ends of the filter units flowsdownwardly between the units by gravity. In this manner the solutionwith the solid particles in suspension is caused to flow in contact withthe entire filtering area of the filter units, so that as the solutionis sucked through the filtering media 13 the solids in suspension aredeposited in an even layer on the entire filter-surfaces Bearing in mindthat the final recipitation takes place in the layers of so 'ds'on thefilter surfaces, it will be understood that this rapid circulation ofthe solution wh lly within the tank '10, by causbe attached to thesuction of the pump ing relatively large proportions of the solu-.

tion to flow in contact with the layers of solids on the filter surfaceswithin a' relatively short time, results in a speedy and effective preciitation. v

In order t at the heavier particles of solids may be prevented fromsettling to the bottom of the tank, a series of agitating propellers 47are provided mounted on a shaft 48 located under thelower ends of thefilter units and in the trough-shaped bottom 49 of the filter tank. Theshaft 48 is driven from the pulley 40 by the belt 50. By keeping thelarger articles of,'solids in agitation with the sma er particles andthe solution, the mixture becomes equalized and in that condition isdrawn 11 through the conduit and distributed over t e upperends of thefilter units. Consequently, as the solution flows down over the filtersurfaces and in contact therewith, the homogeneously mixed coarser andfiner particles of precipitant are deposited over the entire filteringarea of the filter units and the solution flows through the depositedlayers in intimate contact with the large and small particles composingthem.

When a suflicient flow of solution has passed through the filter unitsand it is desired to remove the solids which have accumulated on thefilter surfaces, the flow of solution and precipitant is discontinued,the

pump 19, however, being kept in action until the solution has beenlowered nearly to the 7 bottom of the filter leaves. Each leaf is thenremoved from the filter tank and cleaned, a partial vacuum beingmaintained on the leaf by means of a hose which may 19. During thisclean-up the precipitation will necessarily be imperfect andconsequently lilt) the efiluentsolution from the pump 19 should bereturned to the tank for retreatment. The recovery or clean-up of theprecipitate may be effected without interrupting the operation of theapparatus as a whole, by successively connectin each leaf to the suctionof pump 19 and t en taking the leaf out of thetank for removal of theprecipitate. By keeping the filter leaf connected with the suction ofthe pump 19 the cake of filtrate is not only prevented from dislodgmentduring the transfer but is also dried and so may be more easily handled.

In the form of apparatus shown in Figs. 4 and 5 thefilte'r tank 52 iscylindrical in lit shape and the filter leaves 53 are radially with aconvenient source of power. The mlxture of solution and solids drawn upthrough the conduit 54 by the propeller 55' is prevented agitating theupper of the solution in the tank and is deflected over the u per endsof the filter units 53 by means oi the centrally arran ed bafile 58. Inthis form of apparatus the lter tank is shown with a flat bottomadjacent to which is located an agitator or (propeller with horizontalarms 60 mounte on the up r'end of a shaft 61 connected with a s aft 62driven from the shaft 57. In other respects the ancillary parts of the.apparatus shown 'in Fig. 4 are the-same in construction and functlon asthe corresponding parts'of the preferred form of apparatus, and aregiventhe same reference aracters. The vacuum tank shown in Fig. 1' may bedispensed --with under certain conditions 'of operation and is notillustrated in the form of apparatus shown in Fig. 4.

In both forms of apparatus it will be noted that the centrally arrangedconduit is of substantially the same length as the filter .ment of themeans for agitating and themeans of maintaining the circulation ofsolution wholly within t-he filte'r tank, the object is to-keep thecoarser and finer articles "of solids homogeneously mixed in t esolution, so that they willbe distributed in that relationship over theentire filtering area of from solutions by means of suitable precipi'tants; v .Having thusdescrijbed the invention, we

the filtering units, and so-resultinthe most effective precipitation,

The invention has been; particularly described as applied to therecovery of gold.

an'd'silver from cyanide solutions by means of zinc dust, but it will beunderstood that the apparatus herein described and particularly: pointedout in the claims is applicable to t e recovery of other valuablesubstances claim:-

particles of solids in suspension into the tank, a series of verticallyarranged filter units in the tank, a vertically arrange-id cons duit inthe tank, means for drawing the 'solution in the tank u through theconduit, and means located a we the discharge end of the conduit forpreventing the solution drawn up through the conduit from rupturin -thesurface of the solution in the tank and for directingthe flowingsolution outwardly over the upper ends of the filter units.

2. An apparatus for precipitating and filtering from solution comrising, a tank,

means for introducing a so ution containing particles of solids insuspension into the tank, a series of vertically arranged filter unitssuspended in the tank, a vertically,

arranged conduit in the tank, the upper discharge end ofthe conduit.termina mg below the surface of the solution in the tank,

means for drawing the solution upthrou h I the conduit, and meanslocated above t e discharge end of the conduit for'directing thesolution drawn up through the conduit outwardly overand in contact withthe u per ends of all the filter units so that t e ing area of thefilter units.

3. An apparatus for precipitating and filteri from solution comprising,a cylindrica tank, means for introducmg a solution containing nparticlesof solids in suspension into the ta ,a vertically arranged conduitlocated centrally in the'tank, the discharge opening vofthe conduitbeing located below the surface of the solution in the tank,

a series of'radially arranged filter units in the tank, means fordrawing the solution up through the conduit, and deflecting meanslocated above the discharge opening of the conduit for directing thesolutlon outwardly over the upper ends of the filter units. v

' 4.. An apparatus for precipitating and filtering from solutioncomprising, av tank, means for introducing a solution containing solidsin suspension mto the tank, a series of vertically arranged filter unitssu's nded in the tank, a vertically arran con- ,duit in the tank, theupper discharge end of which is located below the surface of thesolution in thetank, means for drawing the 7 solution up, through theconduit, and a de- 1. An apparatus for precipitating-andfil-vv teringfrom solution com rising, a tank,- means for introducing-a so utioncontaining flector located over the upper end 'of' the conduit forreventing the solution drawn up .th'rou hitllc conduit, from ruguringthe surface 0 the solution in the ta LOUIS D. MILLS.

THOMAS B. GROWE.

so solution will flow down over the entire filter- I

